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Search indexed NASA NTRS and DOE OSTI research on propulsion, heat transfer, battery materials and energy systems. Follow report and document links to the original sources.

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At least 109 records · Page 6
All sourcesNASA NTRSDOE OSTI
NASA NTRS1972

Flow conditions around the exit and downstream of certain stator blading with various trailing edge thicknesses and geometries

The blading investigated was curved back with thick profiles. The variations in flow conditions considered were flow angle and isentropic energy. Experimental data were obtained in a two-dimensional cascade from surveys with a combined angle, total-, and static-pressure probe and from an array of end-wall static pressure taps. Analytical results were obtained from ideal flow theory. The results showed large variations in flow conditions close to the plane of the trailing edge that were largely attenuated at a distance a little greater than one blade pitch downstream of the trailing edge in the direction of flow. The results were affected by the geometry and thickness of the trailing edge. The agreement between experimental and analytical results is generally fair to excellent.

Prust, H. W., Jr.↗
NASA NTRS1985

Through-flow modeling of axial turbomachinery

Through-flow analysis practices are presently evaluated by comparing their results with the flow measured on a single-stage compressor rotor that had been tested at the nominal design flow coefficient of 0.85, using both thick and thin inlet endwall boundary layers. Sufficient experimental data was available for both the required aerodynamic input of the calculations and the detailed assessment of the computational results obtained. It is noted that, while through-flow theory reasonably characterizes many aspects of the flow, the features less well predicted suggest the need for a more precise formulation of the equation, and the inclusion of such often neglected effects as the radial component of blade force and/or the fluctuation terms due to the flow's nonaxisymmetry, as found in the phenomenon of blockage.

Dring, R. P.↗
NASA NTRS1956

Second-order subsonic airfoil theory including edge effects

Several recent advances in plane subsonic flow theory are combined into a unified second-order theory for airfoil sections of arbitrary shape. The solution is reached in three steps: the incompressible result is found by integration, it is converted into the corresponding subsonic compressible result by means of the second-order compressibility rule, and it is rendered uniformly valid near stagnation points by further rules. Solutions for a number of airfoils are given and are compared with the results of other theories and of experiment. A straight-forward computing scheme is outlined for calculating the surface velocities and pressures on any airfoil at any angle of attack

Van Dyke, Milton D↗
NASA NTRS1990

Stability theory for chemically reacting flows

Linear stability theory for chemically reacting (equilibrium and nonequilibrium) flows is applied to study the stability of hypersonic boundary layers under the equilibrium assumption. The results for Mach 15 flow indicate that the second mode instability shifts to lower frequencies, as compared to the perfect gas results. The peak second mode growth rate is also increased for the equilibrium gas model. However, the results for Goertler instability show very little real gas effect. The present theory has been applied to a sphere-cone flight transition experiment performed at freestream Mach of about 20.

Malik, Mujeeb R.↗
NASA NTRS1976

Kinetic theory of turbulent compressible flows and comparison with classical theory

A complete set of turbulent correlations is given in terms of expansion coefficients in a double series of Hermite polynomials of a two-particle correlation in phase space. Only two of these coefficients, corresponding to Reynolds stress and turbulent heat flux, are shown to appear in gasdynamic equations of turbulence. This is accomplished by incorporating the phase-space correlation in the collision integral of Boltzmann's equation and by deriving generalized Navier-Stokes and Fourier transport relations. In contrast to the classical formalism, the simple expression remains invariant in form whether the flow is compressible or not. Nevertheless, a bilinear transformation of fluctuating quantities shows that the two formalisms are identical with regard to terms of double correlations. The kinetic theory justifies nonexistence of the higher-order correlations characteristic of compressible-turbulence equations in the classical regime.

Tsuge, S.↗
NASA NTRS1974

Secondary vorticity in axial compressor blade rows

A theoretical investigation of secondary flow in compressor blade rows is presented. Formulas for calculating secondary flows in annular cascade blade passages are derived. The influence of the relative rotation vector on secondary velocity perturbations, using recent developments in shear-flow theory, is examined. A method of calculating the flow through successive blade rows is given and a comparison is made with experimental results.

Dixon, S. L.↗
NASA NTRS1983

Magnetohydrodynamic and gasdynamic theories for planetary bow waves

A bow wave was previously observed in the solar wind upstream of each of the first six planets. The observed properties of these bow waves and the associated plasma flows are outlined, and those features identified that can be described by a continuum magnetohydrodynamic flow theory. An account of the fundamental concepts and current status of the magnetohydrodynamic and gas dynamic theories for solar wind flow past planetary bodies is provided. This includes a critical examination of: (1) the fundamental assumptions of the theories; (2) the various simplifying approximations introduced to obtain tractable mathematical problems; (3) the limitations they impose on the results; and (4) the relationship between the results of the simpler gas dynamic-frozen field theory and the more accurate but less completely worked out magnetohydrodynamic theory. Representative results of the various theories are presented and compared.

Spreiter, J. R.↗
NASA NTRS1985

Magnetohydrodynamic and gasdynamic theories for planetary bow waves

A bow wave was previously observed in the solar wind upstream of each of the first six planets. The observed properties of these bow waves and the associated plasma flows are outlined, and those features identified that can be described by a continuum magnetohydrodynamic flow theory. An account of the fundamental concepts and current status of the magnetohydrodynamic and gas dynamic theories for solar wind flow past planetary bodies is provided. This includes a critical examination of: (1) the fundamental assumptions of the theories; (2) the various simplifying approximations introduced to obtain tractable mathematical problems; (3) the limitations they impose on the results; and (4) the relationship between the results of the simpler gas dynamic-frozen field theory and the more accurate but less completely worked out magnetohydrodynamic theory. Representative results of the various theories are presented and compared.

Spreiter, John R.↗
NASA NTRS1955

General theory of conical flows and its application to supersonic aerodynamics

Points treated in this report are: homogeneous flows, the general study of conical flows with infinitesimal cone angles, the numerical or analogous methods for the study of flows flattened in one direction, and a certain number of results. A thorough consideration of the applications on conical flows and demonstration of how one may solve within the scope of linear theory, by combinations of conical flows, the general problems of the supersonic wing, taking into account dihedral and sweepback, and also fuselage and control surface effects.

THEORIES - FLOW - LINEAR↗
NASA NTRS1984

An experimental and theoretical analysis of the aerodynamic characteristics of a biplane-winglet configuration

Improving the aerodynamic characteristics of an airplane with respect to maximizing lift and minimizing induced and parasite drag are of primary importance in designing lighter, faster, and more efficient aircraft. Previous research has shown that a properly designed biplane wing system can perform superiorly to an equivalent monoplane system with regard to maximizing the lift-to-drag ratio and efficiency factor. Biplanes offer several potential advantages over equivalent monoplanes, such as a 60-percent reduction in weight, greater structural integrity, and increased roll response. The purpose of this research is to examine, both theoretically and experimentally, the possibility of further improving the aerodynamic characteristics of the biplanes configuration by adding winglets. Theoretical predictions were carried out utilizing vortex-lattice theory, which is a numerical method based on potential flow theory. Experimental data were obtained by testing a model in the Pennsylvania State University's subsonic wind tunnel at a Reynolds number of 510,000. The results showed that the addition of winglets improved the performance of the biplane with respect to increasing the lift-curve slope, increasing the maximum lift coefficient, increasing the efficiency factor, and decreasing the induced drag. A listing of the program is included in the Appendix.

Gall, P. D.↗
NASA NTRS1989

Unsteady stagnation-point heat transfer during passage of a concentrated vortex

The unsteady boundary layer due to a single rectilinear vortex filament approaching a 2-D stagnation point is investigated. Assuming the vortex remains far from the surface, incompressible potential flow theory is used to determine the time dependent inviscid flow field. The unsteady boundary layer equations are solved by an alternating-direction-implicit finite-difference method. Two mechanisms which cause fluctuations in heat transfer are the unsteady velocity field in the boundary layer and secondly, the unsteady total temperature at the edge of the boundary layer. The relative importance of these mechanisms is dependent upon the total temperature fluctuations relative to the imposed temperature difference. As a vortex approaches a stagnation point it may be forced to one side of the stagnation line or the other, depending on its initial position. Results are presented for both of these cases.

Rigby, David L.↗
NASA NTRS1974

A note on the influence of axial velocity ratio on cascade performance

A thin airfoil quasi-two-dimensional potential flow theory has been used to analyze cascades with axial-flow contraction. Attention is centered on the flow turning of a lattice of foils as measured by the deviation angle. The influence of both axial-flow acceleration and foil thickness on the deviation angle is summarized in plots that should be useful for design purposes. It is shown that the effect of axial-flow contraction is larger when the foils are relatively far apart than when they are close together. The influence of axial velocity ratio across the cascade changes markedly with the stagger angle. These effects are essentially unaltered due to foil thickness.

Wilson, M. B.↗
NASA NTRS1976

Experimental and theoretical study of flow fields surrounding boattail nozzles at subsonic speeds

An investigation has been conducted to determine the effects of jet exhaust on the subsonic flow surrounding boattail nozzles with and without separated boundary layers. Measurements of local Mach number and flow angle were made at free-stream Mach numbers of 0.60 and 0.80. Jet exhaust flow was simulated with a solid sting and with high-pressure air at jet total pressure ratios of 3 and 5. The results show that there are strong effects of the wave structure of the jet on the external flow field. The local Mach numbers and flow angles for the models with solid sting jet simulators were in good agreement with subsonic inviscid/viscous flow theory. The theoretical method does not, however, adequately predict the flow about the models with high-pressure air jets.

Putnam, L. E.↗
NASA NTRS1961

Study of Flow Over Oscillating Airfoil Models at a Mach Number of 7.0 in Helium

A wind-tunnel study of unsteady flow at a Mach number of 7 in helium has been conducted on several sting-mounted wedge, double-wedge, and flat-plate airfoil models with three different leading-edge radii. The data were obtained by taking high-speed schlieren motion pictures of the decaying motion of the model as it was released from an initial deflection. The shock-wave position observed on the sharp-leading-edge models during the oscillation was compared with that obtained by use of unsteady flow theory as well as steady-state theory. Comparison of theoretical results indicated that no unsteady-flow effects exist over the range of reduced frequencies k, 0.007 less than equal than k less than or equal 0.030, studied experimentally. The experimental results confirmed this finding as no unsteady-flow effects were detected in this reduced-frequency range. Comparison of shock-wave positions measured for the blunt models with those calculated by steady-state methods indicated fair agreement.

Arman, Ali↗